A mule is a type of shoe that typically has a closed toe and is backless or has no strap around the heel. These types of shoes are designed for a foot to easily slide into or out of the shoe. Such shoes are desirable because the slip-on style is convenient as it takes a short time to put the shoes on with no buckles or shoelaces to tie, and mules can be worn with any style of dress from casual to formal.
Mule-type shoes, however, are not typically worn for activities, such as sports, that involve running, jumping, climbing and quick starting and stopping motions. One reason is that mule-type shoes are not convenient or useful for such activities because the shoes can easily fall off of a person's foot or feet during these activities. Thus, most athletic shoes used for sports, running and other similar activities have a closed heel to securely hold the shoes on a person's feet. Many people that wear mule-type shoes, therefore, typically have to carry a pair of closed heel shoes with them to change into if they are going to be doing athletic activities such as sports. Needing an extra pair of shoes for such activities can be burdensome and inconvenient, as well as expensive.
Additionally, many people manually convert regular closed heel shoes into mule-type shoes by forcibly smashing the heel downward against the footbed with their feet. In particular, children will forcibly bend the heel down so that they can easily slip their closed heel shoes on and off their feet without having to spend time tying their shoelaces or securing straps. Forcibly bending the heels down on shoes that are not constructed to be bent down causes the material forming the heels to deteriorate and lose support, ultimately destroying the shoes.